2 Answers
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No, there is nothing you can do about that (except not using JPEG 2000, of course). JPEG 2000 requires much more CPU power to en- and decode than plain JPEG files. So even including a third party decoder will probably not bring a huge improvement.

You can create a UIImage from JPEG 2000 data. The decoding process will be slower than decoding JPEG, but once it's decoded, displaying it in a UIImageView should be just as fast as any other format. If you have lots of JPEG 2000 images, you may want to cache the decoded images in NSCache.